Recent investigations of children have detected adverse effects of exposure to lead at levels previously thought to be innocuous. Irreversible neuropsychological effects have been reported with blood lead levels as low as 10 .mu.g/dL, and several million asymptomatic children are known to have as much as twice that concentration. The most recent revision of standards by the U. S. Public Health Service Centers for Disease Control lowered the recommended intervention level from 25 .mu.g/dL to 10 .mu.g/dL, a concentration at the lower extreme for accurate monitoring by currently practical laboratory techniques. Consequently, a need has emerged for more sensitive and reliable biomarkers of very low body burdens of lead.